Summary Parkinson's disease (PD) is a debilitating progressive degenerative movement disorder associated with loss of dopaminergic (DA) neurons in the substantia nigra (SN) along with the accumulation of ?-synuclein (?-syn) in the brain, activation of microglia, production of inflammatory cytokines/chemokines, infiltration of CD4+ T-cells, and neurodegeneration. The most potent therapy, L-dopa, does not block disease progression, and the mechanism of the progressive nature is unclear. Calpain, a cysteine protease regulated by calcium, plays a pivotal role in SN and SC (spinal cord) degeneration in PD, and its role in ?-syn aggregation, activation of microglia, T cells and their migration indicate calpain to be crucial in promoting the inflammatory process and disease progression. While calpain-1 cleavage of ?-syn promotes synuclein aggregation in PD-like diseases, the precise involvement of the two major calpain isoforms, calpain-1 and calpain-2, in ?-syn presentation to CD4+ T-cells remains unknown. Preliminary studies here identified a subtype of CD4+ T cells in MPTP mice, which was abolished by calpain inhibitor, suggesting that activation of calpain and CD4+ T cells may play critical roles in the inflammatory process and disease progression in PD. Preliminary data also suggest that siRNA-mediated knockdown of calpain-2 diminishes antigen presentation by human B-cells and inhibits activation of CD4+ T cells. Thus, we hypothesize that activation of distinct calpain isoforms may favor expansion of a subtype of ?-syn-reactive CD4+ T cells in PD-like disease. We also hypothesize that calpain inhibition may attenuate ?-syn aggregation and expansion of inflammatory T cells, reduce inflammation and support neuronal survival and improved outcome in PD patients. Two specific aims are proposed to test the hypothesis: (Aim 1) To investigate whether activation of calpain-1 or calpain-2 is linked with microglial presentation of ?-syn to CD4+ T cells resulting in disease progression and neurodegeneration in PD-like disease in mice. (Aim 2) To determine whether inhibition of calpain-2 reduces microglial presentation of ?-syn and generation of pathogenic CD4+ T cells, attenuating disease progression in mouse models of PD. The goal of this study is to investigate the role of calpain-1 and calpain-2 in generating ?-syn-reactive pathogenic CD4+ T cells, and whether a subpopulation of CD4+ T cells from MPTP mice can induce PD-like disease in immunodeficient mice. Studies are planned to determine whether deletion of calpain-1 attenuates ?-syn aggregation and expansion of CD4+ T cells using calpain-1 knockout (KO) mice. In addition, the role of calpain-2 inhibitor will be assessed in the study of alteration of inflammatory CD4+ T cell response and production of cytokines/chemokines in calpain-1 KO mice. Testing the effects of distinct calpain isoforms in the generation of ?-syn-reactive pathogenic T cells and induction neuronal death and degeneration may lead to development of a novel approach for treating PD as well as other neurodegenerative disorders.